This application is related to DE 198 37 041.5 filed on Aug. 14, 1998, which is incorporated by reference in its entirety for all purposes.
The invention relates to a process for preparing ready-to-use solutions by direct gas introduction.
A semiconductor factory is conventionally currently supplied with chemicals by delivery of chemicals, which are concentrated to a greater or lesser extent, mainly concentrated hydrochloric acid 36%, concentrated ammonia water 28% and concentrated hydrofluoric acid 40%, via tanker trucks or other suitable containers (up to 20 m.sup.3). Generally, they serve for the preparation of cleaning solutions such as SC1 or SC2 (SC=standard clean). They are used for removing particulate, organic and metallic contaminants, which accumulate on the wafer surface during processing. These chemicals are distributed to the individual workplaces ("wet benches") via a central chemical supply system. This type of supply requires the use of a multiplicity of expensive chemical containers, combined with a high expenditure for installation, maintenance and quality assurance measures at the semiconductor manufacturer's and its suppliers etc., since the required specifications (anions, cations, organic impurities) vary within the lower ppb range. To solve these problems, most recently, there has been a conversion to generating on-site the concentrated chemicals for wafer cleaning. That is to say, from the corresponding gaseous anhydrides and high-purity water, the corresponding concentrated solution is produced directly by mixing in suitable processing apparatuses, generally trickle columns equipped with the appropriate accompanying units, such as pumps, heat exchangers etc.
A plant of this type for producing concentrated solutions is described in the company brochure "Turnkey Chemical Distribution System" from L'Air Liquide (distributed at Semicon '98).
The customary technique includes a number of disadvantages:
The concentrated solutions produced are highly corrosive and therefore highly susceptible to contamination. PA0 The amounts of heat liberated during the dissolution of ammonia, hydrogen chloride or hydrogen fluoride in water must be dissipated. PA0 To achieve the saturation end point, multistage absorption and cooling are generally necessary. PA0 To achieve the purities required, high-purity gases must be used or technical quality grades must be further purified.